Got one on my TE. Uses usual plug, just unplug wiring for the nav iv and plug in your 550 lead. Then use the rear of the nav iv mount to fix your 550 mount on.
But
To get it fitting so I could see the instruments I had to position it far to the left on the mounting bar and dremelled out a bit of the mount so it's partially on the curve of the top left part of the bar. And I needed longer screws..... Otherwise fine